The overall objective is to investigate how nerve growth factor (NGF) controls the morphological development of sympathetic and sensory neurons. For this purpose, a new culture preparation was devised which permits long-term, local exposure of different parts of a neuron to different chemical environments. Among the findings with this preparation was that sympathetic axons did not grow into regions lacking NGF even though other parts of the neuron had access to an abundant supply. In addition to this local control of axon growth, preliminary experiments suggested that axon branching and formation of neurotransmitter release sites are promoted by local NGF. It is proposed to investigate the local effects of NGF in individually visualized, sympathetic neurons; the intent is to define more sharply the character of local control of axon elongation, branching and varicosity formation by NGF. Similar studies are planned on sensory neurons, which are also NGF-sensitive, but have different morphology. Finally, it is proposed to investigate local control of sympathetic development, in vivo as well as the distribution of NGF in vivo.